Carrier Phase Estimation Algorithm In Coherent Optical Communications System

With the upcoming of “Broadband Strategy of China”, the conventional IM/DD optical fibercommunications system can not meet the requirements of higher-capacity of data transmission inthe future. Coherent optical communications once booming in the1990s, not only can providethe high speed transmission rate, but also can efficiently compensate the various distortions ofthe system by using DSP. With the continuous improvement of the computational speed of digitalsignal processor, coherent optical communications has become one of the most competitivetechnologies in the next-generation high speed optical communications network.Under this background, the core technology of carrier phase estimation in the coherentoptical communications system is systematically studied. Principles of Mth-power algorithm,DA ML algorithm and adaptive DA ML algorithm are the focus of this theies. The impacts of theparameters involved in algorithms on the performance of phase estimation are simulated andanalyzed. Besides, the optimal parameter values are analyzed. The space complexity and timecomplexity of Mth-power and DA ML are studied for the first time. The most obvious feature ofDA ML is the introduction of a reference phasor. DA ML is not only better than the Mth-powerin the performance of phase estimation, but also overcome the nonlinear operation and phaseambiguity in the Mth-power scheme. DA ML algorithm is a totally linear computational scheme,which is feasible for on-line processing and the high speed optical communications system. Theconcept of equalization enhanced phase noise(EEPN) is introduced in the carrier phaseestimation. We present the generation mechanism of EEPN and EEPN’s value for the FD-FIR.The value of system phase noise is analyzed. The optimum system rate in coherent opticalcommunications system is proposed for the first time, and its value is associated with the ratio ofthe transmitting end laser with the local oscillator laser linewidth. The optimum rate can beeffectively used to suppress the impact of the system phase noise and improve the performanceof system. Finally, we analyze the impacts of EEPN on the carrier phase estimation algorithms.DAML algorithm is more suitable for integrating with the electronic equalization and thelong-haul coherent optical communications.